The present invention relates to a turbocharger for use in an internal combustion engine, and, more particularly, to a turbocharger having a multi-stage compressor.
An internal combustion engine may include one or more turbochargers for compressing a fluid which is supplied to one or more combustion chambers within corresponding combustion cylinders. Each turbocharger typically includes a turbine driven by exhaust gases of the engine and a compressor which is driven by the turbine. The compressor receives the fluid to be compressed and supplies the fluid to the combustion chambers. The fluid which is compressed by the compressor may be in the form of combustion air or a fuel and air mixture.
A turbocharger may also include a two stage compressor with two separate compressor wheels which are carried and driven by a common shaft. U.S. Pat. No. 4,344,289 (Curiel et al.) discloses a supercharger with a two-stage compressor having two compressor wheels which are disposed in a back-to-back orientation relative to each other and carried by a common shaft. The hub portions of the two compressor wheels are configured differently relative to each other, but the overall diameter of the compressor wheels at the outside diameter of the blades is the same. The two compressor wheels and the common shaft appear to be monolithically formed with each other. Since the compressor wheels have the same diameter, the stress capacity of the compressor wheels is limited by the common material from which they are constructed. Moreover, the rotational inertia of the entire compressor assembly can only be altered by changing the geometry of the compressor wheels since they are constructed from a common material.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the invention, a method of configuring a compressor in a turbocharger for use in an internal combustion engine is provided with the steps of: providing a multi-stage compressor including a first compressor wheel carried by a shaft, an axially extending first inlet associated with the first compressor wheel, a radially extending first outlet associated with the first compressor wheel, a second compressor wheel carried by the shaft, an axially extending second inlet associated with the second compressor wheel, and a radially extending second outlet associated with the second compressor wheel; fluidly interconnecting in series the first outlet associated with the first compressor wheel with the second inlet associated with the second compressor wheel using an interstage duct; selecting a total pressure ratio to be provided by the multi-stage compressor; ascertaining a first pressure ratio provided by the first compressor wheel at an operating speed; sizing the second compressor wheel to provide a second pressure ratio, dependent upon the total pressure ratio and the first pressure ratio; determining a stress on the second compressor wheel at the operating speed; determining a temperature within the interstage duct at the operating speed; and selecting a material from which the second compressor wheel is constructed, dependent upon each of the stress determining step and the temperature determining step.
In another aspect of the invention, a method of operating an internal combustion engine is provided with the steps of: providing an exhaust manifold; providing a multi-stage compressor including a turbine carried by a shaft, a turbine inlet fluidly connected with the exhaust manifold, a first compressor wheel carried by the shaft, an axially extending first inlet associated with the first compressor wheel, a radially extending first outlet associated with the first compressor wheel, a second compressor wheel carried by the shaft, an axially extending second inlet associated with the second compressor wheel, and a radially extending second outlet associated with the second compressor wheel; fluidly interconnecting in series the first outlet associated with the first compressor wheel with the second inlet associated with the second compressor wheel using an interstage duct; selecting a total pressure ratio to be provided by the multi-stage compressor; ascertaining a first pressure ratio provided by the first compressor wheel at an operating speed; sizing the second compressor wheel to provide a second pressure ratio, dependent upon the total pressure ratio and the first pressure ratio; determining a stress on the second compressor wheel at the operating speed; determining a temperature within the interstage duct at the operating speed; selecting a material from which the second compressor wheel is constructed, dependent upon each of the stress determining step and the temperature determining step; and rotatably driving the turbine, the first compressor wheel and the second compressor wheel using exhaust gas from the exhaust manifold.
In a further aspect of the invention, a turbocharger for an internal combustion engine is provided with a multi-stage compressor providing a total pressure ratio of between 3.5:1 and 9:1. The multi-stage compressor includes a shaft; a first compressor stage including a first compressor wheel carried by the shaft, an axially extending first inlet associated with the first compressor wheel, and a radially extending first outlet associated with the first compressor wheel. The first compressor wheel has a first diameter (A) and is constructed of aluminum. A second compressor stage includes a second compressor wheel carried by the shaft, an axially extending second inlet associated with the second compressor wheel, and a radially extending second outlet associated with the second compressor wheel. The second compressor wheel has a second diameter (B) and is constructed of titanium or steel. The first compressor wheel and the second compressor wheel have a ratio (A:B) of between 1.15:1 and 2.5:1, preferably between 1.25:1 and 1.6:1. An interstage duct fluidly interconnects in series the first outlet associated with the first compressor wheel with the second inlet associated with the second compressor wheel.